The present invention relates to the fabrication of integrated circuits in substrate processing systems (especially multi-chamber systems). More particularly, the invention provides a technique for synchronizing the operations performed in one chamber with those performed in another chamber in such a system.
Chamber operations can be categorized as either process operations, which are performed with a wafer (i.e. substrate) in the chamber or conditioning operations, which are performed without a wafer in the chamber. Common examples of process operations include deposition, etch, and implantation operations. Common examples of conditioning operations include cleaning, seasoning (i.e. precoating), holding, purging, heating and cooling operations. A seasoning operation is used to deposit a coating on the chamber wall. A hold (or idle) operation serves to delay the performance of the next operation and typically maintains various chamber conditions (such as pressure and temperature). A purge operation is used to flush out of the chamber toxic or reactive gasses left over from one or more previous operations.
A multi-chamber system contains two or more chambers for performing wafer processing operations, one or more robots for transferring wafers between the processing chambers, and one or more transfer chambers which house the robot(s) and are maintained at low atmospheric pressure. Such a system is disclosed and described in U.S. Pat. No. 4,951,601, issued to Maydan et al. and assigned to Applied Materials, Inc., the disclosure of which is hereby incorporated by reference.
Multi-chamber systems are increasingly being used in the fabrication of integrated circuits. Such systems provide advantages over conventional systems, including a reduction in one or more of the following: the number of fabrication steps, the amount of wafer handling and thus the amount of wafer exposure to particulates, cycle time, and fab floor space. However, the use of multi-chamber systems typically requires tighter coordination between the operations performed in the various chambers than is required in comparable substrate processing systems consisting of a series of single-chamber units.
In all multi-chamber systems known to the inventors, individual chambers carry out respective recipes independently of one another (a recipe connoting an ordered set of operations performed as an indivisible group). In other words, events occurring during the performance of a recipe carried out in one chamber do not affect the performance of a recipe being carried out in another chamber.
For various performance reasons, discussed in the detailed description below, it is often desirable for the termination of an operation in a first chamber's recipe to coincide with the termination of an operation in a second chamber's recipe. For example, it might be desirable for a first chamber to carry out a hold operation (during which the chamber conditions are maintained but wafer processing suspended) as long as a second chamber is carrying out a clean operation. The current approach to ensuring simultaneous termination of the hold and clean operations requires specifying a fixed length for the operations. This approach suffers from various problems including the following:
1) The time required for a suitable clean operation depends on a range of factors (such as the number and types of chamber operations performed since the last clean) and is, thus, likely to vary over time. Specifying a fixed length clean operation typically will result in undercleaning and/or overcleaning; the former having a negative impact on subsequent processing operations and the latter resulting in corrosion of the chamber hardware (and thus shorter chamber lifetime and greater down time for the entire processing system because of more frequent chamber replacements). Thus, techniques allowing for variable-length clean operations (such as eadpoint detection, whereby the endpoint of a clean operation is detected as a dramatic change in the chamber concentration of a particular chemical spies) are often preferable to techniques using fixed length clean operations.
2) Even with fixed operation periods, the terminations of the clean and hold operations might not coincide if the termination of the clean operation is delayed for some reason. For example, such a delay could result from the occurrence of a fault condition in the second chamber.
3) Changes in the use of the multi-chamber system containing the first and second chambers may require alteration of the time specified for the clean operation. For example, if the second chamber is used for depositions and the film thickness required for the depositions changes, the time required for an adequate clean will change. En this situation, human intervention (which is both expensive and error-prone) is required to change the time specified for the clean operation and hold operations. This problem is particularly significant for substrate processing systems, such as contract foundries, used to produce many different types of parts.
Because of the above and other similar problems, it is desirable to develop a technique for synchronizing events in one chamber's recipe with events in another chamber's recipe, whereby the termination of an operation (and, in particular, a variable length operation) in a first chamber's recipe could trigger the termination of an operation in a second chamber's recipe.
Another desirable type of inter-chamber synchronization involves causing a recipe to be scheduled for one chamber every time another recipe is schedule for another chamber. For example, a first chamber might perform a clean recipe after processing a certain number (X) of wafers since its last clean recipe. It might be desirable, or even necessary, to suspend normal wafer processing and to carry out a conditioning recipe in a second chamber whenever the first chamber is carrying out a clean recipe. One technique for achieving this result involves maintaining a count of the number of wafers processed in the second chamber since the last time the conditioning recipe was performed, and performing the conditioning recipe every time the count reaches X.
The above technique may not cause the conditioning recipe in the second chamber to be carried out at the desired times (i.e. whenever the first chamber carrying out its clean recipe) because:
1) The count of the number of wafers processed in the second chamber since the last time the conditioning recipe was performed may not equal the number of wafers processed in the first chamber since its last clean. This would occur if one or more of the wafers were processed only in one of the chambers but not in the other.
2) A fault condition might require a clean of the first chamber before X wafers have been processed since the last clean.
Current solutions to the above problem involve constant human monitoring. What would be desirable is a more reliable and less expensive technique for ensuring that a particular conditioning recipe is carried out in a second chamber every time a clean recipe is carried out in a first chamber.